To reduce a weight of products, easily achieve mass production of products using injection molding devices, etc., there has been an increasing demand for resin called engineering plastic which can replace metal. To efficiently lump together resin pellets which are raw materials for this resin molding process such that the resin pellets have a target weight and charge the resin pellets into bags, a packer scale has been conventionally used.
The packer scale is one kind of an automatic weighing apparatus which adjusts a weight of objects such as powdered products (detergent, fertilizer, etc.), or granular products (resin pellets, cereal, feeding stuff, etc.) so that a predetermined target weight is attained, and charges the objects into containers such as bags. The packer scale is typically constructed to include components such as throw-in cut gates, hoppers, hopper gates, load cells and actuators. According to intended uses, a variety of packer scales have been proposed.
For example, a technique is known, in which the objects are fed to hoppers using timer charging by controlling open time of cut gates (see Patent Literatures 1 and 2).
There is also proposed an apparatus intended to achieve high-speed weighing and highly-accurate weighing of objects by volume throw-in of the objects to hoppers and a combination of a plurality of complementary throw-in volumes which are different in volume ratio (e.g., 1:2:4:8) (see Patent Literatures 3, 4, and 5).
There is also proposed an apparatus intended to achieve high-speed weighing and highly-accurate weighing of objects by volume throw-in of the objects to hoppers and complementary throw-in of the objects using loss-in discharge (see Patent Literature 6).